1. Field of the Invention
The present invention relates to electrical power distribution systems for vehicles, and more particularly to a circuit protection scheme for an electrical power distribution system using an electronically resetable circuit breaker arrangement.
2. Description of the Related Art
Vehicles, airborne, terrestrial or marine, that incorporate an electrical generating system to power their functions generally have a primary and a secondary electrical distribution system. The primary electrical distribution system usually handles the high wattage power produced by generator(s), and directs that power to a secondary electrical distribution system. The secondary electrical distribution system divides the incoming power among many small electrical circuits that feed individual systems and equipment on the vehicle. The secondary electrical power distribution among systems and equipment of the vehicle is typically achieved through a number of circuit breakers mounted collectively in circuit breaker panels that provide for downstream wire and circuit protection. The circuit breaker panels are within reach of the vehicle operator. Additionally, such secondary power distribution systems may also include remotely located switching devices such as relays or semiconductor devices, located in other panels or control units, and used to turn on and off loads in response to operator commands.
Traditional vehicle designs use circuit breaker panels that are physically located in the operator compartment of the vehicle. The circuit breakers are typically made of simple, low cost, highly reliable thermo-mechanically activated components that open automatically and autonomously when subjected to an overcurrent condition. Such circuit breakers are manually closed or reset, by tactile operator action. Although simple and effective, such circuit breakers add considerable weight and manufacturing cost due to their associated circuit breaker panel assembly weight. In addition, large and heavy wires and cables are needed to realize system connections between equipment bays, the operator compartment, and the location of circuit breakers and electrical loads.
Significant manufacturing cost reduction can be achieved if the secondary electrical distribution system, including the circuit breaker function, is located in close proximity to the systems and equipment of a vehicle. The cost reduction comes from decreased size of interconnecting wire gauges, smaller wire lengths, and lower installation design costs for fewer secondary power panels installed. In this case, however, the operator is remotely located from the circuit breakers during vehicle operation, and hence the operator cannot manually reset circuit breakers or deactivate circuits when needed.
However, the cost reduction mentioned above can still be achieved if the operator of the vehicle can control the circuit breaker panel function remotely. Solid-state circuits containing solid-state power controllers (SSPCs) have attempted to address this need. An SSPC is a semiconductor based switching device that typically relies upon a metal-oxide semiconductor field effect transistor (MOSFET) as the switching element. When incorporated into an Integrated Secondary Power System (ISPS), the SSPCs can provide a manner of remote switching and circuit protection through electronic communication.
SSPCs, however, have their own set of problems that tend to offset their advantages. More specifically, SSPCs are made of high cost semiconductor materials. The actual switching device in an SSPC (e.g. MOSFET) exhibits an increased “on state” resistance when compared to a circuit breaker. That increased resistance leads to increased voltage drop to downstream services and increased power dissipation, leading to increased weight and cost for additional thermal management systems. In addition, a short circuit failure mode occurs very often in SSPCs. Because the semiconductor devices used as SSPCs, such as MOSFETs, do not inherently emulate the basic function of circuit breakers, complex controllers and algorithms are needed to program the SSPCs so that their behavior mimics that of a circuit breaker. Reliability of SSPCs is lower due to the increased part count that comes with complex controllers. Reliability of SSPCs is also impacted by excessive heating and/or insufficient cooling conditions typical to vehicle environments. Therefore, while the SSPCs enable remote control, they do so at a significantly higher cost, reduced electrical performance, and low reliability.
A few publications have studied circuit protection schemes for electrical power distribution systems. One such technique is described in U.S. Pat. No. 5,440,441, entitled “Apparatus for Protecting, Monitoring, and Managing an AC/DC Electrical Line or a Telecommunication Line Using a Microprocessor.” With the method described in this work, parameters of a switch are recorded by a control system, which then commands the switch to open when recorded parameters indicate an over-current condition. A controlled switch does not however emulate the basic function provided by circuit breakers. Controlled circuit breakers and switches are also used in U.S. Pat. No. 4,964,058, entitled “Power Management and Automation System.”
Another technique is described in U.S. Pat. No. 6,577,963, entitled “Programmatic Resetting of Circuit Breakers.” In this publication however, a priori information about components and their arrangement in the electrical power distribution system is needed to decide on a reset strategy.
Another technique is described in U.S. Pat. No. 4,853,820, entitled “Electronic Circuit Breaker Systems.”. However, in the apparatus described in this work, an automatic reset circuit breaker is not used. Hence monitoring of residual currents passing through the electrical power distribution system is needed, in order to decide when it is safe to restore full electrical operating current to the electrical power distribution system.
A disclosed embodiment of the application addresses these issues by utilizing a hybrid electronically resetable circuit protection system that retains the basic function provided by circuit breakers, does not use solid state devices for circuit protection and switching functions, and can be remotely controlled.